Grey bits are aluminium plates, to which you attach a sharp blade on the leading edge.
You drop it over your lettuce, close the actuator, the lettuce is cut and falls onto the plate. You move the assembly over your harvesting crate and use the other actuator to tip it in.
How did you plan to move the blades? Use high power servos or even a stepper motor with a short leadscrew?
In general it would be enough to move one blade against the other one.
Your ideas are really nice, I will follow your further development and am looking forward how it will work